commit https://github.com/vim/vim/commit/9f5842e63fc63d438cbffcec503e072a06f74dc2 Author: Bram Moolenaar <Bram@vim.org> Date: Sun May 29 16:17:08 2016 +0200 patch 7.4.1857 Problem: When a channel appends to a buffer that is 'nomodifiable' there is an error but appending is done anyway. Solution: Add the 'modifiable' option. Refuse to write to a 'nomodifiable' when the value is 1.

" Vim compiler file
" Compiler:     ATT dot
" Maintainer:	Marcos Macedo <bar4ka@bol.com.br>
" Last Change:	2004 May 16

if exists("current_compiler")
  finish
endif
let current_compiler = "dot"

if exists(":CompilerSet") != 2		" older Vim always used :setlocal
  command -nargs=* CompilerSet setlocal <args>
endif

CompilerSet makeprg=dot\ -T$*\ \"%:p\"\ -o\ \"%:p:r.$*\"